1. Field of the Invention
The present invention relates to a system for purging contaminants from the lens of an instrument, such as a radiation pyrometer.
2. Description of the Prior Art
Radiation pyrometers are widely used for detecting temperatures in applications such as gas turbines, and the standard pyrometers sense radiation through a window or lens that is normally mounted in a tube that opens through a housing into a turbine rotor chamber.
One of the requirements is that the pyrometer lens be kept clean and free of particulate contaminants. Particles deposited on the lens can reduce the energy to the sensor and thereby cause inaccurate temperature measurements. Several purge air designs have been developed to keep particulate contaminants from the lens and the sighting tube, but most have limitations in normal use, for example when the pyrometers are to be mounted with the sighting tube facing in an upward direction where gravity will cause particles to fall down onto the lens and the flow is not sufficient to purge the particles. In some designs, a particle laden compressor air supply is used to "scrub" the surface of the lens, that is, pass over the surface of the lens. Significant particle deposition on the lens occurs as the result of the contaminants from the purge air flow contacting and adhering to the lens as the air passes over the surface.
Other designs provide an air curtain spaced from the lens that is intended to keep the flow of air in a direction to move the particles away from the lens, but during starting and stopping of the turbine in an aircraft, particularly when the pyrometer lens surface is facing upwardly, particles precipitate and accumulate on the lens surface.